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Enhanced Oil Recovery (abbreviated EOR) is a generic term for techniques for increasing the amount of crude oil that can be extracted from an oil field. Using EOR, 30-60 %, or more, of the reservoir's original oil can be extracted[1] compared with 20-40%[2] using primary and secondary recovery.

Enhanced oil recovery is also called improved oil recovery or tertiary recovery (as opposed to primary and secondary recovery). Sometimes the term quaternary recovery is used to refer to more advanced, speculative, EOR techniques.[3][4][5][6]

Contents

How it works

Enhanced oil recovery is achieved by gas injection, chemical injection, ultrasonic stimulation, microbial injection, or thermal recovery (which includes cyclic steam, steamflooding, and fireflooding).

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Gas injection

Gas injection is presently the most-commonly used approach to enhanced recovery. A gas is injected into the oil-bearing stratum under high pressure. That pressure pushes the oil into the pipe and up to the surface. In addition to the beneficial effect of the pressure, this method sometimes aids recovery by reducing the viscosity of the crude oil as the gas mixes with it.

Gases commonly used include CO2, natural gas or nitrogen.

Oil displacement by carbon dioxide injection relies on the phase behaviour of the mixtures of that gas and the crude, which are strongly dependent on reservoir temperature, pressure and crude oil composition. These mechanisms range from oil swelling and viscosity reduction for injection of immiscible fluids (at low pressures) to completely miscible displacement in high-pressure applications. In these applications, more than half and up to two-thirds of the injected CO2 returns with the produced oil and is usually re-injected into the reservoir to minimize operating costs. The remainder is trapped in the oil reservoir by various means.

Chemical injection

Several possible methods have been proposed. Some successful applications are injection of polymers, which can either reduce the crude's viscosity or increase the viscosity of water which has also been injected to force the crude out of the stratum. Detergent-like surfactants such as rhamnolipids are injected to lower the capillary pressure that impedes oil droplets from moving through a reservoir.

Ultrasonic stimulation

It has been proposed to use high-power ultrasonic vibrations from a piezoelectric vibration unit lowered into the drillhead, to "shake" the oil droplets from the rock matrices, allowing them to move more freely toward the drillhead. This technique is projected to be most effective immediately around the drillhead.[3]

Microbial injection

Microbial injection is part of microbial enhanced oil recovery and is presently rarely used, both because of its higher cost and because the developments in this field are more recent than other techniques. Strains of microbes have been both discovered and developed (using gene mutation) which function either by partially digesting long hydrocarbon molecules, by generating biosurfactants, or by emitting carbon dioxide (which then functions as described in Gas injection above).[7]

Three approaches have been used to achieve microbial injection. In the first approach, bacterial cultures mixed with a food source (a carbohydrate such as molasses is commonly used) are injected into the oil field. In the second approach, used since 1985[8], nutrients are injected into the ground to nurture existing microbial bodies; these nutrients cause the bacteria to increase production of the natural surfactants they normally use to metabolize crude oil underground.[9] After the injected nutrients are consumed, the microbes go into near-shutdown mode, their exteriors become hydrophilic, and they migrate to the oil-water interface area, where they cause oil droplets to form from the larger oil mass, making the droplets more likely to migrate to the wellhead. This approach has been used in oilfields near the Four Corners and in the Beverly Hills Oil Field in Beverly Hills, California.

The third approach is used to address the problem of paraffin components of the crude oil, which tend to separate from the crude as it flows to the surface. Since the Earth's surface is considerably cooler than the petroleum deposits (a temperature drop of 13-14 degree F per thousand feet of depth is usual),[10] the paraffin's higher melting point causes it to solidify as it is cooled during the upward flow. Bacteria capable of breaking these paraffin chains into smaller chains (which would then flow more easily) are injected into the wellhead, either near the point of first congealment or in the rock stratum itself.[11]

Thermal recovery

In this approach, various methods are used to heat the crude oil either during its flow upward in the drillhead, or in the pool, which would allow it to flow more easily toward the drillhead.

Economic costs and benefits

Adding oil recovery methods adds to the cost of oil — in the case of CO2 typically between 0.5-8.0 US$ per tonne of CO2. The increased extraction of oil on the other hand, is an economic benefit with the revenue depending on prevailing oil prices.[12] Onshore EOR has paid in the range of a net 10-16 US$ per tonne of CO2 injected for oil prices of 15-20 US$/barrel. Prevailing prices depend on many factors but can determine the economic suitability of any procedure, with more procedures and more expensive procedures being economically viable at higher prices. Example: With oil prices at around 130 US$/barrel, the economic benefit is about 100 US$ per tonne CO2.

Examples of current EOR projects

In Canada, a CO2-EOR project has been established by EnCana at the Weyburn Oil Field in southern Saskatchewan. The project is expected to inject a net 18 million ton CO2 and recover an additional 130 million barrels (21,000,000 m3) of oil, extending the life of the oil field by 25 years.[13] (When combusted, this extra volume of oil will produce nearly 60 million ton CO2, so in this case carbon capture and storage in combination does not result in a net reduction in atmospheric CO2). Since CO2 injection began in late 2000, the EOR project has performed largely as predicted. Currently, some 1600 m3 (10,063 barrels) per day of incremental oil is being produced from the field.

Potential for EOR in United States

In United States, the Department of Energy (DOE) has estimated that full use of 'next generation' CO2-EOR in United States could generate an additional 240 billion barrels (3.8×1010 m3) of recoverable oil resources. Developing this potential would depend on the availability of commercial CO2 in large volumes, which could be made possible by widespread use of carbon capture and storage. For comparison, the total undeveloped US domestic oil resources still in the ground total more than 1 trillion barrels (1.6×1011 m3), most of it remaining unrecoverable. The DOE estimates that if the EOR potential were to be fully realised, State and local treasuries would gain $280 billion in revenues from future royalties, severance taxes, and state income taxes on oil production, aside from other economic benefits.

See also

References

  1. ^ DOE - Fossil Energy: DOE's Oil Recovery R&D Program
  2. ^ http://www.energy.ca.gov/process/pubs/electrotech_opps_tr113836.pdf
  3. ^ Hobson, Hobson; Eric Neshan Tiratsoo (1975). Introduction to petroleum geology. Scientific Press. ISBN 0901360074, 9780901360076.  
  4. ^ Walsh, Mark; Larry W. Lake (2003). A generalized approach to primary hydrocarbon recovery. Elsevier.  
  5. ^ Organisation for Economic Co-operation and Development. 21st century technologies. 1998. OECD Publishing. pp. 39. ISBN 9264160523, 9789264160521.  
  6. ^ Smith, Charles (1966). Mechanics of secondary oil recovery. Reinhold Pub. Corp.  
  7. ^ "Tiny Prospectors", Chemical & Engineering News, 87, 6, p. 20
  8. ^ http://www.saione.com/aboutpdl.htm Biography of Philip Lauer
  9. ^ www.titanoilrecovery.com Titan Oil Recovery (Beverly Hills CA) webpage
  10. ^ http://www.en.allexperts.com/q/Geology-1359/2009/1/temperature-underground.htm#6 Geology Q/A website
  11. ^ WMI International, Houston TX 77092; (713) 956-4001
  12. ^ Austell, J Michael (2005). "CO2 for Enhanced Oil Recovery Needs - Enhanced Fiscal Incentives". Exploration & Production: The Oil & Gas Review -. http://www.touchoilandgas.com/enhanced-recovery-needs-enhanced-a423-1.html. Retrieved 2007-09-28.  
  13. ^ http://www.netl.doe.gov/publications/proceedings/01/carbon_seq/2a1.pdf Department of Energy website

External links


Study guide

Up to date as of January 14, 2010

From Wikiversity

Mainly the following process are done for Enhanced oil recovery

→Water injection

→Gas injection

→Reducing residual oil saturation, SOR (alcohol, polymers, surfactants injection)

→Thermal: steam injection (to heating of the reservoir to lower the viscosity)

However, all the above techniqes are dependent on reservoir conditions and crude properties.

Water injection/water flooding

Conventionally, based on the type of production and nature of reservoir the following patters are followed an injection well. Once the primary energy of the reservoir tends to deplete it becomes necessary to maintain the pressure inside the reservoir to achieve optimum production and maximise ultimate recovery. In such condition the pressure maintenance can be done by injecting water into the reservoir which is compatible to the formation water present in the reservoir through several water injection wells. Such kind of operation is known as water flooding/Water injection.

In this process, the primary objective is to fill the voidage created by the produced oil fractions thus avoiding the reservoir pressure to decrease with the increased production. When the water is injected in the reservoir, it tends to push the oil towards upwards thus increasing the life and the ultimate recovery of the reservoir. Water injection and water flooding are quite similar terms the only difference being the level at which injection water is being discharged and the displacement phenomena

Water injection:

In water injection operation, the injected water is discharged in the aquifer through several injection wells surrounding the production well. The injected water creates a bottom water drive on the oil zone pushing the oil upwards. In earlier practices, water injection was done in the later phase of the reservoir life but now it is carried out in the earlier phase so that voidage and the secondary gas cap in the reservoir are not created. Using water injection in earlier phase helps in improving the production as once secondary gas cap is formed the injected water initially tends to compress free gas cap and later on pushes the oil thus the amount of injection water required is much more. The water injection is generally carried out when solution gas drive is present or water drive is weak. Thus for better economy the water injection is carried out when the reservoir pressure is more than saturation pressure.

The selection of injection water {displacing fluid} depends upon the mobility rate between the displacing fluid {injection water} and the displaced fluid {oil}

DISADVANTAGE OF WATER INJECTION

• Reaction of injected water with the formation water can cause formation damage.

• Corrosion of surface and sub-surface equipment.

Water flooding:

In this operation, displacing fluid is injected in the oil zone through the surrounding water injection wells creating an edge water drive flooding oil towards the production well. For better efficiency, the pressure of the reservoir should be such that no secondary gas cap is formed. Water flooding is generally more effective than water injection when no voidage is being created. Water flooding in other regards is similar to water injection including selection parameters of the displacing fluid, the only difference being the displacing phenomenon. However, in practice the above patterns are not necessarily followed It is to be noted that water injection and water flooding are essentially the same process, however, while in the case of former we inject the water in the water zone of the reservoir, in the latter we inject it directly into the hydrocarbon zone


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